As the damping device of this type, there is known one disclosed in JP 10-184757 A. This damping device is a device provided as a brace between poles of building structures. Specifically, the damping device includes a rod member coupled to one structural body, and a housing member provided to cover the rod member and fixed to another structural body. The rod member has an outer peripheral surface provided with a helical thread groove, and a nut member that is freely rotatable with respect to the housing member is threadedly engaged with the thread groove. Further, a cylindrical rotor housed within the housing member is fixed in the nut member, and the rotor has an outer spherical surface facing an inner peripheral surface of the housing member so as to form a containing chamber for viscous fluid.
In the damping device structured as described above, when the rod member advances and retreats in an axial direction with respect to the nut member along with vibration applied between the two structural bodies, the nut member converts an axial motion of the rod member into a rotational motion, and the rotor fixed in the nut member is also rotated along with the rotational motion of the nut member. At this time, a gap between the outer peripheral surface of the rotor and the inner peripheral surface of the housing member is formed as the containing chamber for the viscous fluid. Thus, when the rotor is rotated, a shear friction force in proportion to a rotational angular speed of the rotor is applied to the viscous fluid in the accommodation chamber. As a result, heat is generated in the viscous fluid. In other words, in this damping device, vibrational energy between the structural bodies is converted into rotational energy, and further, energy of the rotational energy is converted into thermal energy. As a result, the vibrational energy transmitted between the structural bodies is attenuated.